Recent advances in solid-state technology coupled with marked decreases in the cost of hardware have provided the impetus to reexamine computer architectures. The von Neuman computer and other early stored-program computers were constrained to single data-stream/single-instruction-stream sequential organization primarily because of economic considerations (flip flops were of the order of $100 each). Today, however, with flip flops priced under$0.25 each, hardware costs are rapidly approaching the point where both horizontally distributed (array structures) and vertically distributed (hierarchical structures) information processing architectures are not only feasible, but economically practical.